text:
Would this hovercraft be stable?
Would this two-rotor hovercraft design work? The bold black line is weighted metal on the lower to stable it. If it helps, this is a human sized hovercraft.
Would it work if:

prop1 lift > prop2 lift
prop1 lift = prop2 lift
prop1 lift < prop2 lift

The difference between prop1 and prop2 lift should be in a range of 0-30%

NOT TO SCALE, assume that lower weighted bars are equidistant from middle of hovercraft.

A hovercraft rides on an inflated air cushion and is inherently stable.  Do you mean a twin-rotor helicopter instead?

If all you want to do is fly it around a few inches off the ground, then putting a skirt around it reduces the power requirement dramatically.  And voila!  There's your hovercraft.

In other words, use the ground effect, too much weight, it won't fly.  Good one, Camille.  I would also explore the stabilizing effects of the rotor "disks".  They seem to help on bicycles.

As a matter of interest, are hovercraft on topic on Aviation? They are normally considered ships.

Yes - it can work. Colin Furze (UK inventor & TV personality) built an essentially similar device. Skip to about 1:40 to see some of the problems he had.

What a death trap!

What kind of motor do you think he uses?

You can see that there are two rather cantankerous and unreliable two strokes. Double the risk of failure!  And when one goes, even if you stay close to the ground, it flips you over and if you're lucky, you won't have a limb removed when it goes through the running engine's flimsy netting that is all that is between you and your future nickname, "stumpy", during the crash.  This Fruze chap seems to have about the same risk tolerance profile as BASE jumpers, who are addicted to near death experiences.

However the answer to “would this be stable” is a NO – the thing is not stable, and it cannot be made stable. It is controllable (barely), but not stable. No helicopter is stable in hover. It could be made stable by converting it into a hovercraft, that is adding the skirt all around it, which would also reduce the power requirement.

@Jan Hudec. Would not the 2 rotating "disks" add stability. They seem to on a bicycle.  Yes, this is a hovercraft.  A little high drag would give a "righting" force while in motion.  The main issue seems to be engine reliabilty.  Great start for this inventor.

@RobertDiGiovanni, bicycle is not stable. When moved out of the centred position, the deviation grows unless corrected. The gyroscopic effect slows down the deviation increase a bit, which makes it more controllable, but cannot change the way the feedback works. The same applies to rotorcraft.

@Jan Hudec was hoping for a full answer from you, sorry they closed this one. The gyroscopic effect does indeed make it more controllable, and that is the key.

If the weight is located low enough, it should have "pendulum stability", just like this toy --

If the props are running at different speeds and generating different amounts of lift, then (assuming that is a top view not a side a view), the pilot's weight will need to be off-center to compensate.

"Pendulum stability" doesn't work.  The toy you mention is stable because the center of drag is behind the center of mass.

We're going to get to the bottom of this pendulum thing.  Too much "fallacy" and Pavlovian dv's.  Needs work.

In other words, an object in an unaccelerated state will have a "pendulum" effect, but Mark is correct, drag, and thrust line also play a role.

Put a little drag above the prop and watch what happens to hover stability.  May be another reason the Army liked to put a radar bulb there.

@Mark -- sure "Pendulum stability" works. This related answer goes into some detail about how the "pendulum effect" of a low CG contributes to roll stability-- https://aviation.stackexchange.com/questions/77971/when-a-paraglider-pilot-applies-brake-on-one-side-and-maintains-the-brake-pressu/77996#77. See main body, 3rd footnote, and addendum. It's also not hard to see how putting the center of drag way above the CG would contribute to pitch stability  or speed stability -- in fact arguably this is essentially the only source of pitch stability or paragliders, yet they can be flown hands off.

@Mark -- I don't know the exact mechanism at play in the case of the helicopter toy, but obviously there is one. The rocket case is totally different, nothing to do with what I am talking about, because the aerodynamics of the rocket nozzle don't change significantly when the rocket is tilted relative to the flight path, but that's not true of the rotor disk. Amazing that Goddard would suffer from such a misconception. Anyway this link is more relevant-- see especially the 1st paragraph -- https://en.wikipedia.org/wiki/Keel_effect

@RobertDiGiovanni -- re your last -- more likely because that allows the radar to see over the ridgeline that the helicopter is hiding behind.

That's the primary reason, it seems to work.

@Mark -- consider also the question -- why do pilots find a model airplane to be more stable in a nose-up "hover" maneuver (see https://www.instructables.com/id/Want-to-fly-3D/ , https://www.youtube.com/watch?v=aqOEwCzR3YQ ) if the CG is well AFT?  Do the dynamics have anything to do with the dynamics of the rotor-on-the-stick toy?  Could be grounds for another ASE question, to explore one of the many facets of "pendulum" stability.  The amazing thing about the rotor on stick toy is that it is stable both climbing and descending-- fascinating--

@quietflyer, the keel effect, airplane pendulum stability, and the like are all about the relative positions of the center of mass and various aerodynamic surfaces.  But your answer is suggesting that the relative positions of the center of mass and the center of thrust are important, which is the classic rocket pendulum fallacy.

@Mark  -- "all about the relative positions of the center of mass and various aerodynamic surfaces"-- is not the same true of the prop-on-a-stick toy?. Consider-- would these other toy helicopters fly just as well if the rotor blades were below rather than above the center of mass?  https://www.youtube.com/watch?v=sV5EFlAmfIA , https://books.google.com/books?id=IyEDAAAAMBAJ&pg=PA148&lpg=PA148#v=onepage&q&f=false (pages 148-150)

@Mark -- I don't fully understand the mechanism at play here (could be the basis of another ASE question?) but I think it is fundamentally different than a jet or rocket engine.

@Mark -- I my try to formulate some of the above comments into a question for SE, maybe I'll post in Engineering rather than Aviation to try to get a different community's perspective, haven't decided yet.  Or Physics.  Not sure which would be better.


text:
Is this aircraft legal in Canada?
is an aircraft like this legal in Alberta, Canada? It's basically a human sized quadrocopter. If so do you need any license?

That looks like a great way to make mince meat of someone's legs...

This is an EHang 184 autonomous passenger drone photographed in 2017.
You don't need a pilot's license to fly it, because you don't fly it.

It has preset routes and the passenger selects the intended destination. The vehicle will then start automatic operation, take off and cruise to the set destination before descending and landing in a specific spot. A ground-based centre will monitor and control the entire operation.

Transport Canada hasn't yet figured out how to certify and license such a ground-based centre.  Even so, it's a moot question whether this aircraft is legal in any sense at all in Canada, because no ground-based centre has been built there yet.

One reason the ground facilities haven't been built yet may be that it's not permitted (yet?) to operate the thing in Canada. It's similar with Segways in several European countries, there are no dealerships because they're not legal to operate.

If a human being gets into this and selects a destination, surely that means that, legally, the human is the pilot, doesn't it? The person is both occupying and controlling the aircraft, after all; the fact that the controls are very unusual doesn't seem like it would be legally relevant.

The human is the pilot just like a subway passenger who's bought a ticket from A to B is the conductor.  They can't see-and-avoid. They have no responsibilities. They can make almost no decisions based on what they observe. They haven't been trained in what to observe. They might deploy a parachute, just like the straphanger can yank the emergency brake.

It's not possible to tell for certain based just on this one picture, but I don't see any reason why it wouldn't be. Unlike the US, Canada doesn't recognize the concept of an ultralight helicopter, so you'd need a regular helicopter license to actually fly it.

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text:
Does an increase in lift always cause an increase in lift-induced drag?
An increase in lift causes an increase in drag. Is it always true? I am confused with two points.

Lift increases with an increase in airspeed but induced drag reduces with an increase in airspeed.
Higher aspect ratio wings generate greater lift but create less induced drag.

This question is not very clear.  It should be narrowed down to one specific question.  Give some thought as to whether you really mean to be asking about lift, or about lift coefficient.  Also about what constraints you intend apply-- constant angle-of-attack?  Constant airspeed?  Straight-and-level flight?  At present it looks like some constraints would apply to some parts of the question and other constraints would apply to other parts of the question.

When looking at statements like these, it's important to consider which parameters are varied and which parameters remain fixed.
Let's get this out of the way first by correcting your statements:

Lift increases with increase in airspeed with constant angle of attack but induced drag reduces with increase in airspeed with lift force remaining constant
Higher Aspect ratio wings generates greater lift with constant wing surface area but creates less induced drag with lift force remaining constant.

As you can see, each half of your statement refers to a different scenario. The bottom line is that for lift generation, it's more efficient to give a small change of velocity to a large air mass, than a large change of velocity to a small air mass (because force is generated by momentum change which is linear in velocity, and induced drag is due to the kinetic energy imparted on the air mass which is quadratic in velocity).
When flying fast or with slender (high aspect ratio) wings, you affect a larger air mass every second. You can do two things: either keep your angle of attack constant and get a lot of lift out of the air mass, or in case you don't want to do aerobatic maneuvers, you decrease the angle of attack until lift once more equals weight, and get less induced drag.

Thanks for giving more clearity, it helped me a lot.

Lift increases with increase in airspeed but induced drag reduces with increase in airspeed.

If you keep weight ($W$) constant, the total lift ($L$) does not change with change in airspeed ($V$). $L=W$ for quasi-steady flight, right?
What is changed is the lift coefficient, $C_L$. As speed increases, $C_L$ decreases. Induced drag coefficient ($C_{D_i}$) is related to the square of lift coefficient:
$$C_{D_i}=\frac{1}{\pi e A}C_L^2$$
where $e$ is the efficiency factor (related to wing shape), and $A$ is aspect ratio.
The total induced drag ($D_i$) as a function of speed is:
$$D_i=\frac{2W^2}{\rho V^2 S \pi eA}=\frac{2W^2}{\rho V^2 \pi eb^2}$$
where $b$ is the wing span, $\rho$ is air density and $S$ is the wing reference area. As you can see, the induced drag itself decreases with increasing airspeed for constant weight.

Higher Aspect ratio wings generates greater lift but creates less induced drag

Higher aspect ratio wing does not generate greater lift. It just generates more efficient lift, where efficiency here means less induced drag (see first equation, notice how $C_{D_i}$ decreases with increasing $A$). Note: efficiency here ignores structural penalties, skin friction drag and stall characteristics, which are adversely impacted with higher aspect ratio.

Can you define the variables more explicitly? What are $W,L,S,e,b$? I guess $V$ is airspeed and $\rho$ is air density?

@WaterMolecule Thanks, it's done.

For people like me who have studied physics, but not much aerodynamics, this clarifies things a lot. +1

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text:
Can a CFI give training outside the US in a non-N registered aircraft?
My question is if a US CFI can give instruction in other countries with an airplane that's not registered in the US (N) (as long as he has certifications to fly those airplanes in other countries)?
Must he be a flight instructor as well in those other countries where the airplane is registered?
The perfect example would be a US CFI who is also rated as a CFI in Argentina.
Can he give a Flight Review or training required towards a US PPL certificate in Argentina (with an airplane registered in Argentina)?

Your question seems to be about a US CFI instructing in other countries, yet the first sentence refers to regulations about a "required" airplane for instruction and registration issues. Then your last question is about a flight review in an non-N-registered aircraft. Can you please clarify what your question is really about? Are you asking about the CFI's licensing, about using a specific aircraft, or something else? Maybe this makes sense to others, but I'm really lost on what you're asking about.

Looking at the edit history, I think the title edit added to the confusion. Are you asking about a US CFI giving flight instruction in the US in a non-US-registered aircraft? (for example: your friend flew his German registered plane to the US and you want to take flight instruction in the US in it?)

Guys, sorry for the confusion, I've just updated the post. This would be a US CFI giving instruction in a foreign country towards a US certificate in a foreign aircraft

Makes a lot more sense now! (don't know the answer, but at least I understand the question ;)

Sorry, @FreeMan, and thanks for reading the question

I can not find any prohibition against a US FAA certificated flight instructor giving instruction in a foreign country for a US FAA issued pilot certificate or endorsements. Title 14 of the Code of Federal Regulations Part 61.51 specifically allows a CFI to give instruction in a foreign aircraft registered in a country that is a member state of ICAO. Part 61.41 specifically allows a foreign CFI from a country that is a member state of ICAO to give instruction.
So, this implies that a US CFI can give instruction in a foreign country for a US FAA issued pilot certificate or endorsements. Just as long as the CFI has authorization to fly the foreign registered aircraft in the country of question. Depending on the country, they may need authorization to fly for hire. Depending on the country, they may need authorization to instruct as well. This may only apply to instructing for the issuance of a certificate or endorsement for that country.
So, at the very least, instructing in an aircraft of foreign registry in a foreign country for a US certificate may only require foreign validation of the CFI’s pilot certificate. But, maybe not their instructor certificate.

§61.41 Flight training received from flight instructors not certificated by the FAA.   (a) A person may credit flight training
toward the requirements of a pilot certificate or rating issued under
this part, if that person received the training from:
(1) A flight instructor of an Armed Force in a program for training
military pilots of either—
(i) The United States; or
(ii) A foreign contracting State to the Convention on International
Civil Aviation.
(2) A flight instructor who is authorized to give such training by the
licensing authority of a foreign contracting State to the Convention
on International Civil Aviation, and the flight training is given
outside the United States.
(b) A flight instructor described in paragraph (a) of this section is
only authorized to give endorsements to show training given.
§61.51 Pilot logbooks.   (j) Aircraft requirements for logging flight time. For a person to log flight time, the time must be
acquired in an aircraft that is identified as an aircraft under
§61.5(b), and is—
(1) An aircraft of U.S. registry with either a standard or special
airworthiness certificate;
(2) An aircraft of foreign registry with an airworthiness certificate
that is approved by the aviation authority of a foreign country that
is a Member State to the Convention on International Civil Aviation
Organization;
(3) A military aircraft under the direct operational control of the
U.S. Armed Forces; or
(4) A public aircraft under the direct operational control of a
Federal, State, county, or municipal law enforcement agency, if the
flight time was acquired by the pilot while engaged on an official law
enforcement flight for a Federal, State, County, or Municipal law
enforcement agency.
§61.195 Flight instructor limitations and qualifications.   A person who holds a flight instructor certificate is subject to the
following limitations:
(a) Hours of training. In any 24-consecutive-hour period, a flight
instructor may not conduct more than 8 hours of flight training.
(b) Aircraft Ratings. Except as provided in paragraph (c) of this
section, a flight instructor may not conduct flight training in any
aircraft unless the flight instructor:
(1) Holds a flight instructor certificate with the applicable category
and class rating;
(2) Holds a pilot certificate with the applicable category and class
rating; and

Yes, I've been reading the same regulations... So a US CFI is just needed for the practical test recommendation, other than that an applicant can request a PPL checkride with experience done with a non US CFI outside of the US

There have been ads for US FAA CFI employment in the Middle East for training in the Cessna 172. This may be due to this loophole. At least I call it a loophole. It may be an intentional oversight by the FAA and ICAO. Also, when I pursued certificate validation in South Africa, the flight school there actually offered a program to get FAA and EASA certification. I believe you still had to go to the US or Europe for your checkride.

@IvanParra - As far as needing a US FAA CFI recommendation for the checkride, Part 61.39 states, “(6) Have an endorsement, if required by this part, in the applicant’s logbook or training record that has been signed by an authorized instructor who certifies that the applicant—“ It is a little ambiguous on what “authorized“ means. Normally, they would use the word “certificated”.Especially since the checkride endorsement is only attesting to the fact that training has been accomplished and the applicant is ready.

Yes you are right, but a foreign CFI hasn't an IACRA account to sign the application form

§61.1 has the definition of "authorized instructor".  It excludes foreign CFIs.§61.41 also alludes to the fact that foreign CFIs cannot sign off on practical tests.

@wbeard52 - That is where the ambiguity lies. Part 61.1(b)(iii) opens the door for someone without an FAA CFI to give instruction. Then, 61.41 (a)(2) specifies that a foreign CFI can give training. As far as the alluded to prohibition, I think that is also ambiguous.

I agree that a foreign CFI in their home country can provide instruction that qualifies for the aeronautical experience for FAA certificates and ratings.  What these foreign CFIs cannot do is to prepare them for and sign off as the recommending instructor on the 8710.  Personally, I would never sign off an applicant for a certificate or rating without flying with them for a minimum of three hours as required by the FARs as preparation for the practical test.


text:
Why is the ILS16 approach at KSKF not available in my Garmin 430W?
I am doing flight instruction on the San Antonio area (Texas) and I've been shooting different approches on the vecinity airports.
One of the approaches I usually execute is the ILS 16 at KSKF, which is a military and civilian airport. Yes you can land there and do fuel on the self service pump.
Everything was okay until the last garmin database update in which they removed the ILS approach. When you select the approaches on the GPS the only available ones are the RNAV approaches. I looked into the NOTAMs and there is nothing published there, I am still able to request the approach and do it with the VHF Nav Instruments, but was cool for students to monitor what was going on on the GPS as well.
Does anyone know why the approach is not able to be selected on the GPS?
Note: The GPS Database is current

This is a good question, although it might be best to contact Garmin support. It could be an error or other issue with their database or software. The ILS16 approach is there for me in Garmin Pilot, FWIW.

Thanks for oyur answer

There are two ILS approaches for runway 16. Both of them had amendments on 13 Aug 20. Therefore, the IAP charts that were in the database are no longer valid. They expired. It would be interesting to know the effective date of your last Garmin update. That could affect what approaches you are able to see.
I am unable to pull up the former IAP charts at this time. It would also be interesting to see what has changed. At the KTKI airport, the decommissioning of the MELISA NDB was enough to require a complete change of the ILS approach. Melissa was the Final Approach Fix. You were to notify ATC when you were Inbound inside of the FAF. The NDB has been replaced by the JIPUK waypoint.
This is a good lesson for new pilots. Read the entire IAP chart (including the borders) and check the effective dates.

Hi Dean, sorry I tried to modify your comment instead of mine. I've just clarified that the GPS database is current. Thanks

@IvanParra - Hey, no problem. Though, my question still is when was the effective date of the database. If the database effective date was 10Aug20 and the chart effective date is 13Aug20, there is a chance that the chart will not show until the next update. If memory serves me correctly, they update every 28 days.

I have to check that, thanks for your answer. Although, thinking about it,  we always keep the DB updated, so, if it was on the previous DB why it is not on the new DB, there shouldn't be a gap between expiration of one DB and release date of the other one. Anyhow, I will check

@IvanParra - it is not the expiration date of the previous database versus the effective date of the new database you should check out. It is the expiration date of the old IAP chart versus the effective date of the new database. Did the chart expire between the effective date of the new database and the future effective date of the next database release? When a chart expires, Garmin May make the chart unavailable for use. Even between updates. I know that Foreflight does.

No, the chart is still available on foreflight and the DB was updated with an effective date that is after the chart changes. I have sent an email to Garmin

@IvanParra - Curious, you will have to post the answer when you hear back from Garmin. By the way, I was talking about the old expired chart being no longer available in Foreflight. The updated/amended chart is available.

I will thanks!!

I finally received an answer from Garmin, which wasn't very helpful
Garmin's answer:

Hello, we verified that both ILS approaches for RWY 16 (Z and Y) show up on our GNS430w with the current Navigation data '2010'. Maybe the issue you had was resolved with the latest map update.


text:
Can I fly the LNAV MDA when the GPS is set up for LPV?
I am going to do my CFII checkride in a few weeks and my DPE wants to do RNAV approaches to satisfy the Non-Precision and Precision approaches tasks on the PTS/ACS.
According with the Instrument ACS an RNAV (GPS) approach with LPV minimums can be used to satisfy the precision approach task as long at it has a DH lower than 300 ft. I don't have a problem with that, the airport has an LPV approach with LPV minimum of DH 250 ft.
Now for the non-precision approach, I am going to use the same approach but flying the LNAV minima. So my question, since I haven't flown LNAV minima since my IFR training, my question is: Can I fly the LNAV MDA even if the GPS annunciator is on LPV mode? I guess the answer is yes, so, is there any consideration when doing that?
And just for future applicants, an LPV approach with greater than 300 ft DH can be used to satisfy the Non-precision approach task on the ACS (instrument ACS  page A-17).

Welcome to aviation.SE! LPV and LNAV/VNAV glideslopes aren't always the same so I'm not sure that it would be safe to do what you're describing. But I may have misunderstood your question, could you edit it to explain why you would want to that? If we understand the scenario then someone may be able to give a better answer.

Also, please specify if you are doing a practice approach under VFR, or if you have been cleared for an IFR approach.

Thanks for your answer, I've just did it

Thanks for the clarification, that helps.  It didn’t answer my VFR vs IFR question though.  My answer would be that if VFR it shouldn’t matter.  If IFR I would probably at least advise the controller if I planned to fly the LNAV approach, just so they wouldn’t be surprised by the ratcheting step down, but I’m interested in what others might say because I am still kind of new to GPS approaches.

Yes, I don't know if it's going to be VFR or IFR. I guess it will be VFR and I am just going to simulate that I don't have LPV but LNAV, therefore descend to the MDA until the MAWP. Thanks

ATC will clear the pilot an a specific approach.  What minima they use is not determined by ATC.  Whether the pilots do step downs with an LNAV approach or a CANPA style approach with LNAV/VNAV or a full LPV approach is of no consequence to ATC.

What type of GPS are you using?  It may be possible to reduce the level of service from LPV to LNAV with a click of a button.  There is that feature on the FMSs I use.

I am using a garmin 430W is it possible to do that?

GPS approaches are designed for you to fall back to LNAV if a 'higher' precision option like LPV fails during the approach. Just like going from ILS to localizer only if the glideslope fails.
The Instrument Procedure Handbook p. 4-26 says:

Flying a WAAS LPV approach requires an aircraft with WAAS-LPV
avionics. If for some reason the WAAS service becomes unavailable, all
GPS or WAAS equipped aircraft can revert to the LNAV MDA and land
safely using GPS only, which is available nearly 100 percent of the
time.

So you can just ignore the vertical guidance and fly the LNAV step downs using lateral guidance only from the GPS, and your regular altimeter (not your GPS) to identify altitude.
If you haven't done it already (or recently), I'd suggest practicing it before your checkride to see how your avionics behave. You might get alerts that you have to ignore and they could be distracting. It would be best to get a feel for that ahead of time rather than experience it for the first time with an examiner sitting beside you.
You can also just check with your examiner in advance that they're comfortable with what you want to do.

Yes, I am going to do that, thanks!


text:
Why are some airports not allowed as IFR alternates, even if conditions there are VFR?
Why are some airports disqualified for use as an alternate (as listed in a approach procedure for that airport (A N/A)), when there is a provision in part 91 that an airport without an instrument procedure can be used if descent from MDA and under basic VFR conditions are expected using the 1-2-3 rule?
Example: I19 (Greene Co. Airport near Dayton, OH) has a disqualification (A N/A) listed in the procedure. Yet 11 miles away, I73 (Moraine) has no procedures and as I know it there is no specific disqualification.  Albeit, you could only use Moraine for an alternate if descent from MDA and under basic VFR is forecast for the area.
So, why can you not use Green Co. if descent from MDA under basic VFR would be possible?

Welcome to aviation.SE! Does this question help? The procedure is not authorized for alternate purposes, not the airport.

There is a little bit of a misunderstanding in your premise. There is a difference between an alternate airport and a diversion airport. An alternate airport is your listed optional destination for the purposes of filing a flight plan. A diversion airport is the airport to which you head when you can not land at your original destination. They may be one in the same. For instance, when you divert to your alternate airport.
It is not that the airport can not be used as an alternate. It is that the approach can not be used to qualify the airport as an alternate. You can not use the standard precision approach, standard non-precision approach, nor non-standard approach alternate minima. You can, however, use the VFR weather minima to qualify the airport as an alternate. That means that both I19 and I73 are treated the same when filing. This is for filing purposes only.
Once airborne, the situation changes. If the weather or any other circumstance dictates a diversion to airport I19, you can use the procedure to shoot an approach down to the IAP minima regardless of if you filed it as an alternate or even if it qualified as an alternate when filing.  Therefore, you could possibly effect a landing at I19 in IMC, but not at I73 in IMC. You could divert to either one in VMC. Even if your filed alternate were an entirely different airport.

I might consider emphasizing that if you go lost com ATC will expect you to go to your filed alternate.  Seems obvious, but I have seen arguments about this...

@MichaelHall - True. I would even argue that an IFR plan is primarily to allow ATC to know where to expect you. Especially during NORDO. That makes your alternate your first (and second if filed) option when you lose Comms and your original destination is unavailable or unsafe. If you are currently VMC when you lose Comms, landing somewhere else is still an option. Just make sure you notify ATC as soon as practicable.

I don't think this answer is 100% correct. For example, if the airport has IAPs and all of its IAPs are listed as "A NA" then you can't use that airport for filing purposes as an alternative. Yes, 91.169's provision for a VFR decent from MEA but that only applies to airports with NO IAPs. I do think this is a bit nonsensical but that is how I read the FARs. Of course, once you are air born you can fly to whatever alternative you want!

In the US, at least, ATC doesn’t have ready access to your filed alternate. The point of the alternate is to force you (the pilot) to find at least one place you are nearly certain to be able to land if needed, and ensure you have enough fuel to get there.

@StephenS  Agreed.  My TraCon friend says ATC does not receive your filed alternate as part of their data stream.   Lost Comms after going missed or when first intended airport is not viable is not a situation expressly defined in https://www.faa.gov/air_traffic/publications/atpubs/aim_html/chap6_section_4.html
TraCon friend also said they REALLY want a NRDO plane out of the system, so finding a VFR option is highly desirable.  If it was solid IMC or a solid deck beneath me, I probably would go to my filed alternate, having already planned and reviewed it.  Less stress...


text:
Why do airplanes sometimes turn more than 180 degrees after takeoff?
Why do sometimes (at least in commercial flights) airplanes do a more-than-180-degrees loop after takeoff, in order to aim at the target direction? See image for an example.
I guess that it is part of the flight plan, but it looks like a waste of fuel and time to me.

Commercial flights are given clearance from ATC to fly specific Standard Instrument Departures (SIDs). In this instance in Venizia, the pilots upon requesting clearance would have been told by ATC to fly the “Vicenza Eight X-ray” (VIC8X) departure, as shown in the purple track below.

Italia AIP - Venezia SIDs1
Your instinct is correct: SIDs are designed to be efficient, not to “waste fuel and time” as you put it.

The primary objective of the design of instrument flight procedures is
to ensure safety while taking into account efficiency and operational
considerations.
ICAO, Doc 8168, Volume I, Part I, Section 2, Chapter 1
The design of SIDs should aim to ensure the safety of aircraft
operations while also facilitating efficient air traffic management.
ICAO Annex 11, Chapter 2, General Provisions

The most important factor however in SID design is safety. Nearby terrain is one of the common big threats to commercial operations. Hence why some SIDs are designed to initially take the flight routing climbing away from the high terrain on departure. A good example of this is Bergamo, Italy - where departures to the North initially turn towards the south on departure before turning back towards the easterly side of the airport (waypoint LEGLO) and continuing enroute northwards.

Italia AIP - Bergamo SIDs1
Back to our example in  Venezia, there is no immediate terrain so it does seem strange that the VIC8X SID was the cleared routing? As the Venezia charts show, a  left turn after departure is an option (green track). The notes at the bottom left of the chart tell us that this departure isn't an option when there is intense military traffic present within the Treviso CTR. So the presence of military traffic would make a left turn departure unsafe due to congested airspace or perhaps limited ATC coverage, hence why the right turn was the only option available.
Terrain, other airports, airspace danger areas or restrictions are other issues of safety which may preclude the flight routing being the most efficient.
For example, London Luton departures to the east: a right turn is made and then 5000ft is maintained - all due to the proximity of London Stansted.

UK AIP - Runway 07 east departing SIDs - initial turn and altitude restrictions are highlighted in yellow
As a pilot myself, I have also had instance where a thunderstorm cell is sitting on the desired departure path, in this instance we may request a completely different routing from those published on the charts. As in many aspects of modern commercial aviation, efficiency is a high priority, but safety always precedes it as required.
Once safety implications are considered, the SID design then might take into account noise abatement. A good example of this is Barcelona, where all departures from runway 24L (southwesterly) make an immediate (quite dramatic) left turn over the sea to climb before turning back towards land. There is a good video on YouTube showing such a departure .

Spanish AIP - Barcelona 24L SIDs - initial turn highlighted in red
However, immediate noise abatement (below ~4000ft) is typically handled by operationally using NADP1 profiles and flying the initial part of the SID slowly and therefore climbing at a steeper gradient (note the "IAS MAX 200" in the Bergamo and Venezia charts).

1 Aeronautical Information Packages (AIPs) are freely available - typically online. In this instance, the Italians have provided the information via an iPad app.

what a great article TY

A couple of reasons for departures such as this are:

terrain. Perhaps the most obvious (but omitted by me and kindly pointed out by Randomhead ). The effect of terrain on departure and arrival routes is often emphasized because it limits the possible routes the departing and arriving aircraft can simultaneously take. More on this in the last item on the list
noise abatement. Departing  aircraft may sometimes fly seemingly irrational patterns due to surrounding residential areas to minimize noise pollution.
other airports and restriction & danger areas. There may be other airports/airfields, industrial sites, powerplants or military areas near the airfield that limit the possible routes.
crossing arrival and departure routes. It may be that the arrival and departure routes to the airport cross each other, and it will be necessary to maintain vertical separation. Since arriving aircraft need to maintain certain glide profile, the departing aircraft may need to make extra maneuvers to gain enough altitude at certain point, or create lateral separation.

In this particular case, I can see two issues: a) Venice is an important tourist destination; tourists don't like being awakened by an airliner thundering over their hotel, and b) turning left immediately will take the aircraft directly over Treviso airport.

Thanks!! One of the reasons I was particularly puzzled by this case is that turning left would actually disturb less the poor Venetians ( ;-) ) and that landings in Venice always happen arriving from southwards, so there shouldn’t be any disturbance. But indeed, I missed that it could disturb the Treviso traffic. Thanks!!

@JörgWMittag a) doesn't make sense since these departures do the exact opposite, but b) is the reason. I can see SIDs in my charts that turn left after takeoff, but they have a note "SIDs may be authorized only if no heavy military traffic within Treviso CTR".

@Bianfable very interesting!

@RiccardoCeccon remember that this way the aircraft will be higher over the city when crossing residential areas, thus less noise.

One other very big (literally!) reason is terrain. Mountains in one direction means you need to turn in the other direction unless you have lots and lots of extra climb performance.

@Bianfable In my region we also have many tourists but it's the residents, not the tourists, who complain about the noise from the airports. And the ones who get airplanes flying low over their homes complain much more than the ones who have airplanes high over their homes.

@randomhead: terrain is often a factor, but in this specific case, the terrain is pretty much 100% flat in all directions.

@rob74 in this case yes, but the question is a general one, venice is just an example.


text:
Why do some A320s have double-bogie landing gear?
I believe this is actually a rare sighting, but why do some A320s such as the VT-ESD have double-bogie landing gear? Does Airbus have a specific reason for making such A320s?

Update: Found an image in the former Indian Airlines livery,

It may be for operating out of airports where the per-wheel loading is lower. Having more wheels distributes the load more allowing the aircraft to operate out of lower quality runways.

Wikipedia says "Indian Airlines used its first 31 A320-200s with double-bogie main landing gear for airfields with poor runway condition which a single-bogie main gear could not manage" but does not cite a source.

Maybe this will help: https://forums.jetphotos.com/showthread.php?43569-A320-double-bogie-main-gear-an-oddity

I'm surprised that was an option on the A320.  Does it require modifications to the wheel well and the aux gear doors for this?

@CarloFelicione I don't think the A320 can be retrofitted with double bogey landing gears. Airbus has definitely made a certain number of A320s that way, so the wheel well and aux doors must be larger

Air India is the only carrier with that kind of landing gear in the A320 due to India's low pavement classification number back when those A320s were ordered. In other words, more tires distribute the load over a larger area.

Originally ordered by Indian Airlines in the early 90s.

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text:
How can I find out the best time to practice within towered airspace?
I would love to practice within towered airspace (approaches, touch and goes, ect.) However, I do not want to upset operations within the airspace.
What is the best way to determine when the best time to practice these maneuvers would be? Should I contact both the tower and TRACON?

Non-commercial towered airports are good at about midday.

Good info.  How about commercial?  Particularly class C?

From what I know about KMHT (Manchester-Boston Regional Airport), the traffic is more consistent there but evenings are usually more busy.

As well as asking someone directly, you should also check the A/FD: some airports have restrictions on training flights or T&Gs at certain times.

@Pindlife Great point!

Simplest answer: Call the tower. Or ask instructors/schools in the area if the controllers care when you arrive and want to practice. Usually if you arrive during the busiest time, you'll likely be accommodated as best as they can, but there's a chance you could be told to just do a full-stop taxi-back operation if that helps out or told to go fly around elsewhere for a bit.
It depends on what airport you're thinking about going to. If you want to go to ATL, well, you'll be vectored in a gap, and told go as fast as you can for as long as you can, and be told to land(or if you go around, expect a long delay to find a new gap). If it's just a general aviation airport, anytime is fine.

Great info - thanks :)

Yeah, I don't think ATL would be too happy about you requesting to do touch-and-gos there. You might get some laughter just before the "Request denied," though.

@reirab It's published in the AFD, for the no T/Gs, and many other large mostly Class B airports it's explicitly stated, no T/Gs and/or practice approaches.

@slookabill Indeed it is. The $9/gal 100LL price also gives a good indication of how much they appreciate light aircraft landing there. :) Student pilots are also banned completely from ATL, IIRC.

@reirab - although still not quite as hostile as Heathrow's "Just go away" attitude to GA :p

I did most of my training at a towered airport in Class D airspace (KPNE). From my experience there is no "best time" (although there are times when the airspace is more empty) and for what it's worth I found it better to train when the airport was busy as it offered me the chance to practice some real world scenarios.
Running laps in the pattern when no one was around did not really build up my communication skills with the tower as they basically would just clear you for the option every time. When there were other planes in the area they might extend a leg of your pattern or have you do a 180, and these scenarios were better practice in my opinion. Crowded radio frequencies also keeps you on your toes and gets you better practice (especially if there are some similar tail numbers in the area).
You will not be upsetting operations by any means. ATC is there to handle you and frankly it's always good to practice being diverted (if that's what happens) in a busy airspace so you will know how to handle it when you get out on your own missions.
Class C/D space airports generally run a lot of large private traffic and some scheduled carriers. I found that KPNE and KABE (if I wanted to practice in class C) were heavier later in the day and early in the morning as would be logically expected. But to be honest there were plenty of times a bunch of planes would come in all at once mid day and it would be quiet the rest of the day.
If you are a student pilot (you did not say in your question) you can identify yourself as such when entering the airspace and when getting on with the tower. In most cases it will make them a bit more forgiving if you ask for an instruction repeat or don't understand something.

I did all my training in the NYC area from airports with towers. KMMU and KCDW. There was no such thing as a good time (other than 2am to 5 am). For my first solo, I was number 14 to land. Both of those airports share the same approach control frequency as KEWR. If you want to do an approach, you had to do it in traffic. You'd be the only person doing the LOC or ILS at KMMU/KCDW but you'd be sharing the frequency with non-stop approaches to KEWR.
I'd suggest getting some training with an instructor at a busy airport with a tower.

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text:
What is the purpose of several mandatory stops (RWY AHEAD) at busy airports?

I learned that red signs mean: full stop is mandatory.

Do aircraft have to stop before CAT III 08L sign AND before CATI 26R-08L sign?
What is the purpose of making two stops?
Is the area between these two mandatory stops special?

give way to crossing traffic?

A full stop at a red sign is only mandatory if ATC has not given you explicit clearance to proceed further. Aircraft will be instructed to "hold short" of the runway, and these signs indicate where the aircraft should stop.
The CAT II/III signs are only for holding when CAT II/III operations are active on that runway. This refers to categories of the Instrument Landing System (ILS) that are currently in use. An aircraft only needs to stop at the sign applicable for the current conditions, as instructed by ATC. Generally if an aircraft must stop at the CAT III holding point, they will later be cleared either to take off or line up and wait on the runway. That clearance means they do not need to also stop at the CAT I point.
On page 47 of this ICAO Aerodrome Standards manual there is a table showing the required distances from runway center line for holding positions. For example, a long runway (code 4) would require 75 m normal distance, and 90 m for CAT I/II/III approaches. These numbers increase with runway altitudes over 700 m (2,300 ft) elevation. There are also many other factors in the airport configuration that might require a greater distance.
The different holding points are to ensure that in lower visibility conditions, there is more room for added safety. It also helps to ensure that holding aircraft do not interfere with the precision approach signals. The CAT III holding point is further from the runway to ensure that the guidance equipment will provide CAT III accuracy and avoid interference from aircraft and vehicles. If there is not a clear procedure in effect to keep these areas clear, interference can happen, and the faulty signals can result in the airplane following an incorrect path.

ICAO holding position distances represent only a minimum distances which are subject to other factors. In reality, a holding position might need to be even farther away from the runway. This will depend mainly on the characteristics of the Radio Navigation Aids used at the airport, and of the location of the holding position in respect to the obstacle limitation surfaces.


text:
What are these small jets and large propeller aircraft flying in formation?
I came across the photo below on flightaware.com. The image was taken by someone with, I think, an Ukrainian name: Arkadiusz Cieslak. They piqued my interest as they do not appear to have insignia except for the "B" (cyrillic?) on the tail of the transport plane and a design on the fighters. Any ideas? I'm just curious.

The registration of the Constellation is clearly visible (HB-RSC), and a quick google gives you all kinds of cool pictures. I'm guessing the fighters are F-5s

Knowing this is the livery of the Swiss patrol makes search easy. I like this one. BTW, and to link with a recent question about the carriers around the world: Switzerland carrier in territorial waters.

On a side note, that name (Arkadiusz Cieslak) sounds more like Polish, not Ukrainian (without actually knowing; but this kind of digraphs is typical for Polish).

I hope Mr. Cieslak will forgive me ;)

Looks like you are in trouble.

uh oh. is there a way to change my name on SE?

The design on the belly of the fighters makes it clear that they are from the Patrouille Suisse, the aerobatic team of Switzerland. They use F-5E.
From the comment in the page you linked (or from the aircraft registration HB-RSC, as suggested by @falstro), instead, we see that the other aircraft is the Breitling (hence the "B") Super Constellation:

The Breitling Super Constellation from the Swiss Super Constellation Flyers Association: It is the last Super Constellation in flying condition in Europe.

Thanks Federico. I could see the Swiss livery when I enlarged the images. My old eyes are sore. David

Also, I didn't know Constellations were still in use!

@DavidDelMonte They're not still in use: the plane's essentially a museum piece.


text:
What type are these planes that are flying in formation near Culver City, CA?
My son in law took these images a few days ago in Culver City California. We would like to know what the vintage (WWII ?) planes are, and in the last image, what would cause such a contrail. The last image is a composite of several shots. (Something landing at Edwards was my guess). His guess for the aircraft are that they are all the DB Dauntless.

low altitude contrails are done by a smoke generator see sky writing

The wings apart to rectangular to be a dauntless imho.

This is likely Tiger Squadron, perhaps flying for the Israel Independence Day Festival over Rancho Park in mid May, as detailed on their Facebook page.

My (current) guess is that it may be a
Nanchang CJ-6

The Nanchang CJ-6 is an aircraft designed and built in China for use
  by the People's Liberation Army Air Force (PLAAF) as a basic trainer.

Round nose.
Sufficient number airworthy.
Rectangular wing shape.
Main gear folds inwards and the nosegear backwards which seems to fit when I zoom in your pictures.

and they do airshows:

(source: riversideca.gov)
Coincidentally, the upper-left aircraft #43 also appears in your pictures (first picture, rightmost aircraft). Another below of her below:

update: as Cardinal said above, "This is likely Tiger Squadron, perhaps flying for the Israel Independence Day Festival over Rancho Park in mid May, as detailed on their Facebook page."

The CJ-6 appears to have a fairly straight-across (perpendicular to the fuselage) leading edge, whereas the photos from the OP seem to indicate a leading edge that is more swept-back.

@MrWonderful I think it's a visual thing from the angle reinforced by the aircraft banking. The aircraft above is the same as in the OP's photograph. The tail registration while difficult to make out appears to match.

@DavidDelMonte if you have decided that MikeFoxtrot's answer is correct, please mark that his is the accepted answer. This will "close" this question, helping aviation.se keep a 98%+ answered question rate.

That looks like the Red Stars Aerobatic Team - they fly Yak-52s
http://en.wikipedia.org/wiki/Yakovlev_Yak-52
It is hard to tell from your picture, but the overall look of the team itself, the prominent red stars on one of them, and the rounded tail make me think that's who it is. I tried to find their schedule and see if they would have been in your area, but they apparently don't have a web site.
Here's a video I shot of them in 2009 - https://www.youtube.com/watch?v=0A5qYqcQsxw
OK yes... I found their site. Looks like they had an event in CA this weekend, but not very close to you, and the event was cancelled... so they might have been flying around for fun and practice.
http://flyredstar.org/calendar.php

Definitely not. The aircraft in the photographs don't have rounded tail and do have the main gear mostly covered which Yak52 does not.

Had a look at the Yak52 but dismissed it as @JanHudec said for the landing gear. However, the Nanchang CJ-6 was based on the Nanchang CJ-5 which itself was a license built copy of the Yak 18, which also was the predecessor to the Yak52, so the connection is certainly close.

The thing is, I wouldn't expect a team of those to be over Culver City at any time. When I see a formation like that, I think "what aerobatic teams" and I didn't really think beyond that. They are all very similar. It is very hard to identify planes from photos like these. The planes in the photo look a little long, but they could even be these... http://en.wikipedia.org/wiki/Grumman_F6F_Hellcat   which is a heck of lot more likely than a bunch of Chinese planes.

@Jasmine they are not uncommon. if i read the from the FAA's databsase correctly there appear to be at least 25 in California alone. if you open the photos in a new tab the resolution is pretty good.


text:
What is the difference between component service and inspection?
What is the difference between component inspection and component service? And is overhaul / restoration a service or an inspection?

Servicing is lubrication or replenishment as required for a component to continue in service - greasing, adding oil etc.  Inspection is verification that condition of a component is acceptable, either visually, or using an enhancement method like Xray, ultrasonic, or various non-destructive test methods.
Overhaul/Restoration is disassembly, inspection and replacement of internal parts to bring the unit to some minimum dimensional/performance standard.
The term Restoration is generally associated with MSG-3 based maintenance programs and is something like overhaul but often is restricted to specific components identified in endurance testing, or even just something like a grease charge that requires disassembly to remove/replace, again based on endurance testing.
A restoration doesn't "zero time" a unit; it's more of a mid-life refresh.  MSG-3 based parts can be run forever theoretically, because the whole idea is you run the component until periodic functional testing in the field detects a performance degradation, but parts usually also have a structural life limit imposed on a root component like a housing, based on endurance/fatigue testing.  Once the root component reaches its life limit, the part is scrap.  That clock does not get reset by rebuilding the unit.

Thanks  for the info. Was really needed.


text:
What steps do I need to follow to use my PPL for income?
So I am currently taking my PPL because flying was always a passion. But, as I am sure all who do such can relate, it is an expensive license to hold on to.
None the less we go through simply for the joy of flying. But I am wondering if we can transform, somehow, or how fast could we, make this investment something we could have as a possible weekend job?
So, what would be the path to take starting from a PPL to be able to fly an airplane and also make a profit out of it?
Thank you all for your experience sharing and patience!
PS: Apologies for missing this one out, countries around Europe, though more specifically UK and Portugal :)

In what country? In the US, you can tow gliders and banners with a PPL, but not much else.

It's probably worth mentioning that you'll be competing against other people who also just want to fly for free, or build hours towards other qualifications. Some of those will already have a separate source of income, others might see it as an alternative to a minimum-wage job. It's a tough market.

If you are planning to carry people (skydivers, passengers etc.) the aircraft will need appropriate insurance and to be covered by an Air Operator Certificate, I think

You guys are amazing! Thank you so much for this share of information ^^ I do have a separate source of income, was just thinking if possible to also use this passion as a possible source of income as well or at least break nearly even to its costs.

This depends on your jurisdiction a bit since the nuances vary from country to country but in general to get paid to fly (or get paid enough to break even) you need to have at least a commercial pilots license. This would allow you to get paid to fly. With a CPL you can do lots of things like:

Tow banners
Fly charters
Fly cargo
Fly sight seeing flights
Tow gliders (can be done for compensation with a PPL and proper endorsements as well see Rons comment)

What many pilots go on to do if they are only looking for weekend break even fun, is to get their Certified Flight Instructor ticket and teach others to fly. This is a nice way to make some money, fly some beat up planes, and pass along the hobby to others.
The speed to any licenses is hard to predict. It varies based on your time, money and aircraft availability as well as how good of a study you are. You also need to accumulate the hours required for a CPL which can take time. With good weather and a consistently working and free plane you can get through it in months. If you are a weekend warrior and only have access to busy rental planes and live in an area with weather it can take a few years to get everything done.

You can be paid as a PPL in the US to tow gliders with proper endorsements.

Thank you for all your input! This is great and gives me a way better idea on the path to follow!
I love flying but it is an overwhelming world to go through and I know it takes time to absorb everything and reach a certain level. But I also wanted to understand what was needed in order to try and make a passion investment into something that can also provide, even if just a little :3


text:
Difference Between Air Data Computer and ADIRU on the Boeing 737

Altitude (ALT) Select or 1 – enables altitude reporting from air
data computer No. 1.
(FCOM)

What exactly is this “air data computer”? The FCOM doesn’t seem to provide further details on it. Is the air data computer synonymous with the ADIRU? If so, is “air data computer No. 2” the same as “ADIRU-R”?

The air data computer is not synonymous with ADIRU, but it is one of the two components of the ADIRU:

The aircraft is fitted with two (left and right) ADIRUs which are powered from the AC electrical
busses. Each ADIRU includes an IRS and an air data computer which receives information
from separate pitot static sources. The air data part of the ADIRU provides airspeed, Mach
number, angle of attack (AOA), barometric altitude and temperature data. The IRS part of
the ADIRU uses solid state ring laser gyros and X, Y and Z axis accelerometers to provide
information to attitude, FPV and positional data systems.

(Boeing 737-8AS, EI-GJT, serious incident report by the AAIB, emphasis mine)
Honeywell actually calls it "air data function" rather than "computer":

The ADIRU, the heart of the Air Data Inertial Reference System, has two distinct partitions with independent processors.
The air data function calculates critical air data such as airspeed, Mach, angle of attack, air temperature and barometric altitude.
The inertial reference function provides attitude, heading, ground speed and present position data for use in navigation [...]

(Honeywell - Understanding the ADIRU - Video, emphasis mine)
It is a bit strange that the ADIRUs in the 737 are distinguished by side (left or right) and then Boeing uses air data computer No. 1 and No. 2 (instead of left or right). I couldn't find a source that maps these numbers to ADIRUs, but I think it's likely that ADC No. 1 is in ADIRU-L and No. 2 in ADIRU-R.


text:
Diamond DA42 - Do you need the electric master on to extend landing gear?
For the Diamond DA42 (TDI)
Learning my electric fire emergencies. Would it be wise to extend the landing gear before electric master is turned off?
Does the (hydraulic) gear power pack require the electric master to be on to extend the gear?
I presume if the electric master is switched off, could still extend manually using emergency gear extend lever?

In general you should always follow the emergency procedures described in your POH.
The emergency procedure for an Electrical Fire in Flight does not ask to extend the landing gear:

EMERGENCY SWITCH . . . . . . . . . . . . . . . . ON, if installed
AVIONIC MASTER . . . . . . . . . . . . . . . . . . . . OFF
ELECT. MASTER . . . . . . . . . . . . . . . . . . . . . OFF
Cabin heat & defrost . . . . . . . . . . . . . . . . . . . OFF
Emergency windows . . . . . . . . . . . . . . . . . . . open if required
Land at the next suitable airfield

CAUTION
Switching OFF the ELECTRIC MASTER will lead to total
failure of all electronic and electric equipment. [...]

(DA-42 POH - Emergency Procedures)
In case of a complete electrical failure, the electrical hydraulic pump will no longer function:

In case of a failure of the electrical pump, which is driving the
landing gear actuators, the landing gear can be extended
manually [...]

Even if there is still pressure left in the system, the gear lever will no longer open the valves without electrical power:

The hydraulic pressure for the landing gear operation is provided by an electrically powered
hydraulic pump, which is activated by a pressure switch, when the required pressure is
too low. Electrically actuated hydraulic valves, which are operated with the gear selector
switch, provide the required hydraulic pressure for the movement of the landing gear.

(DA-42 POH - 7.5 Landing Gear)
The checklist for Complete Failure of the Electrical System says:

NOTE
The landing gear uplock is no longer ensured. The landing
gear may slowly extend.
The landing gear can be extended manually according to
3.6.2 - MANUAL EXTENSION OF THE LANDING GEAR.

So it's possible that the gear will already extend without electrical power, but you can always follow the manual extension procedure.

Don't keep the electric master on in a fire to lower the landing gear. First off there's time: In any fire seconds matter, the sooner you eliminate the ignition source for the fire the better chance you have of controlling it and keeping it from spreading. The fumes from an electrical fire are toxic and can impair you very quickly, you really don't want an additional 5-10 seconds worth of it in your cabin.
Also, there's the chance of making the problem worse: Electrical fires are caused when malfunctions cause sparks or excessive heat which start insulation or other components on fire. Electric motors draw significant electrical power, additional load on the electrical system could create more sparks and/or heat.
So do not leave the electric master on while you extend the gear during an electrical fire. Follow the POH procedures and use the emergency gear extension lever which is by the pilot's right knee.

If you are operating 10 miles from an airfield where they are giving you a Basic service (UK) and have you on radar. Surely it would be wise to issue a MAYDAY call followed by a quick ask for a QDM to airfield if required before turning off the electric and avionics master switches. I appreciate your concern about toxic fumes. But surely having some sort of plan to land, other than a farmer’s field, would be sensible? POH: emergency switch > quick plan and RT > electric master and avionics OFF > canopy position 2 > emergency windows open

@GdB. Thanks for your answer by the way. By ‘Don’t do this’, I presume you mean don’t lower the gear

That's exactly what I mean @ob318, and no I wouldn't make a mayday call for the exact reasons above. For all you know the radio is what's on fire! You should always have a chart to hand, and know what your position is on it, don't rely completely on your GPS. With a map and your compass you can navigate to an airfield and use radio out procedures to land. I have the UK Distress and Diversion number programmed into my phone for just in case I have an electrical failure.


text:
Do I have to prove my flight training time abroad when applying for a standalone FAA license?
I have done flight training in Germany and hence hold a German EASA Private Pilot License. For this I did the appropriate flight training which is documented in my logbook. But in Germany these logbook entries are not endorsed by an Instructor, it is the flight school sending the paperwork to the CAA that confirms you fulfilled all requirements.
Now I am in the situation, that I want to get a stand-alone FAA license. The two Part 61 flight schools I enquired so far both stated, that without logbook endorsement, non of the flown hours could be credited for the requirements of 61.109. But I also have German pilot friends that claim they also had no endorsements and that this was no problem while getting the license.
Is there maybe an official position paper of the FAA or something that states in more detail, what a foreign pilot needs to bring to prove being eligible?
And of course I know, that I will need additional training, but hopefully not 45 hours again. Therefore if the assumption of StephenS in the first answer is correct and I can use my logbook to prove part of the 20h DUAL (later night training is endorsed and 2.5h flying with CFIs in the US), then maybe I can reduce the requirement to about 15h. But where does the interpretation of only the 20h DUAL must be endorsed come from and not the SOLO or the rest to 40h? And what about the specific requirements in the section below in 61.109? If I have a cross country which is not endorsed, does it fulfill the requirement or not?
To keep this topic straight on this point, I am aware of all the necessities to start flight training:  Regarding medical, I have a Class 3. Regarding student license, I have a 61.75 validation of my German license with ASEL and Instrument. Regarding Visa I am already staying in the US and working legally on a visa, the flight training is just part time.

Did you get the FAA license issued based on your European license (according to 14 CFR § 61.75)or did you just get training time/flying experience credited toward obtaining a "regular " FAA license? If you used 61.75, was your license and class rating valid/current at the time?

I did both, one after the other. For the 61.75 my class rating was valid, for the stand-alone the time was credited, but based on my logged time overall, not based on 61.75.

Interesting. I have a German PPL-A (originally French) with an expired SEP-Land rating with some experience as a pilot (not student), and I was told I would have to redo the entire training as if I had never flown if I want to obtain an FAA license. They won't transfer (61.75) the expired license, which I understand.

Well I should have written, that I still had a valid class rating when doing the stand-alone and the DPE wanted to see a current validation of my German license, but what I meant is the requirements of the FAA had to be fulfilled by showing I actually did a cross country, had the Solo time, etc. and not just by looking at the German license or the 61.75.

I've been in exactly the same position as you: I had an FAA foreign-based (61.75) private certificate based on a South African PPL and then got a regular, standalone FAA private certificate. As you described, SA instructors don't have to endorse each lesson, they only endorse specific permissions like "authorized for solo flight in the circuit".
To answer your main question, no one cared much about the contents of my logbook. The FBO I (re-)trained at didn't look at it and the DPE didn't either apart from glancing over a few entries and saying "huh, that's different". However, he did check the US pre-checkride endorsements from my CFI in detail (more on that below). So I feel very confident saying that foreign endorsements for individual lessons are simply not required.
If you want an official source, see 14 CFR 61.41:

§61.41   Flight training received from flight instructors not certificated by the FAA.
(a) A person may credit flight training toward the requirements of a
  pilot certificate or rating issued under this part, if that person
  received the training from:
[...]
(2) A flight instructor who is authorized to give such training by the
  licensing authority of a foreign contracting State to the Convention
  on International Civil Aviation, and the flight training is given
  outside the United States.

Since Germany is an ICAO state, all your training there counts and asking for endorsements is a little pointless because you have a German PPL. That means it's obvious that you did actually receive the training :-)
Furthermore, the FAA's instructions to DPEs don't require them to check that every lesson was endorsed, they only require them to check a list of specific pre-checkride endorsements (see section 5-375). And you'll get those endorsements from your US CFI before your checkride anyway.
That's because the wider answer to your question is that getting a standalone FAA certificate requires you to do everything as if you were a student: get an FAA medical, get a student certificate, pass the written test, meet the requirements for the checkride (experience plus endorsements) and then do the checkride. And since you're not a US citizen, you'll need TSA approval for flight training. But all your experience logged outside the US counts towards the FAA's requirements, where applicable.
That might seem like a lot of effort but I highly recommend doing it. FAA certificates never expire, whereas licenses from other countries do. Once you have an FAA certificate, you never have to worry about keeping your German license and medical current.

You can find the detailed requirements for a FAA PPL in Part 61 Subpart E.
The total time of 40 hours can be met by any flight time you have logged, either DUAL or PIC.  (In theory, SIC should qualify too, but I can't think of any legal way for a student pilot to have that.)
DUAL time can only be logged when you are receiving "training" from a CFI, who must endorse each such log entry along with a description of said training (maneuvers, procedures, etc.) in the remarks.  This endorsement is what allows those hours to count toward the 20 hours of "flight training" required for your PPL.
The "solo" time of 10 hours can only be met by flight time where you are the only person in the plane, meaning that it can only be logged as PIC time. PIC time does not need to be endorsed--ever.
Where I think you're getting hung up is that a student pilot cannot legally act as PIC without getting an endorsement before the flight, and those endorsements have limitations.  For instance, my first endorsement only allowed me to fly around the pattern at my home airport, the second allowed me to fly between my home airport and a neighboring airport, and the third was for a specific cross-country trip that I'd previously flown with my CFI.  However, the resulting PIC time was not endorsed by my CFI after those dozen or so flights.
In your specific (and unusual) case, you were able to legally meet the solo time and cross-country time requirements without an endorsement before those flights.  Still, like me, you don't need any endorsements after the flights.  Just logging the PIC time yourself was enough for it to count.
Your records and history will undoubtedly look strange to your CFI (and eventually your DPE), so it's best that you make it easy for them to see which specific log entries you're using to meet each requirement.  I'd suggest marking those entries with sticky flags, noting which FAR(s) they fulfill, and including a translation of the remarks if they're not in English.  Don't note or translate your entire logbook, though; they don't care about anything beyond seeing that you've met the minimum requirements.  And, while it shouldn't matter according to a literal reading of the regs, common sense suggests a preference for time logged in US aircraft (N reg) at US airports (Kxxx).
Finally, FAR 61.103(j) says that any applicant for a US PPL must "Hold a U.S. student pilot certificate, sport pilot certificate, or recreational pilot certificate." There's nothing in the regs that says a validated foreign PPL qualifies, so you'll need to discuss with your local FSDO; if they say it does, it's best to get that in writing so there's no paperwork problems with the DPE on the day of your checkride.


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Could Mach 1.4 be a better design point for SST?
There's been a number of recent proposals for design work on low-supersonic bizjets that would cruise at Mach 1.1-1.6, the common theme being avoiding a sonic boom.
The conventional wisdom is to avoid this range, and either stay subsonic or go all the way to Mach 2+, because you sacrifice some efficiency the moment you cross Mach 1:

Sharp nose and supersonic airfoils result in lower L/D across the envelope.
Thin airfoils add weight and require more fuselage space for fuel tanks.

On the other hand, staying at low Mach avoids a few other penalties:

The 12:1 slenderness of modern widebodies translates well to a low-Mach SST, allowing for a similar cabin layout. This is critical.
Skin temperature allows the plane to be built with the same resins as subsonic airliners.
Less COL shift, higher AR wings, reasonable bypass engines make it easier to meet TO lift and thrust requirements.
Speculatively, cruise altitude might be kept at FL450 to avoid stricter pressurization rules.

What I'm not sure is which set of factors matters more. It's difficult to glean from existing designs, as they're not really comparable between one another.
The Aerion's wing should behave well on landings, and it claims only a 22% fuel penalty for going supersonic. But its slender nose and long tail leave just 18% of its length for the cabin, so it can't be used as an airliner template.
This is probably caused by its role as a status symbol and regulatory weight limits; actual SST managed a proper length cabin, and the 2707 was even planned as a widebody. Thin wings have are also featured in some subsonic proposals, so they're not a total efficiency killer.
I'd imagine a Mach 1.x airliner to be a 779-sized twin, with 788-like seating capacity, area-shaped akin to the Sonic Cruiser, an ogive nose (F-16 style), Aerion-like trapezoid SNLF wings, nacelle engines.
The question is, could a low-Mach SST, if sonic boom was publicly accepted, be closer in efficiency to subsonics than to historic high-Mach designs?
To narrow down the scope, let's explicitly exclude:

Whether there is any market for such an aircraft.
Whether Mach 1.x is fast enough to make a difference.
Engines, as it's a major subject in itself. Just assume a rubber engine matching a loose trend line of TSFC~=0.4*Mach.max.

Leaving in scope the technical subject of the efficiency loss imposed by the aerodynamics of supersonic flight. It comes down to how good a L/D can high-tech airfoils like SNLF and area-ruled widebody provide, with how little compromise on capacity, in the range of Mach 1.1 to 2. Fuel per seat-mile being the figure of merit.
To help set a baseline, I've plotted a mix of historic and calculated numbers for known aircraft:

To put the question in more formal terms, I'm looking to estimate the seat-miles/kg function's behavior for an optimal design in the low-supersonic range.
The red line assumes the worst-case scenario and is based on just stuffing seats into the AS2. The green line represents a best-case scenario based on claims with the Sonic Cruiser as a baseline. The truth is probably in between.

While this question does have some concrete technical components, in its current form, it's a market analysis question -- and too broad to ask here without a thorough re-phrasing and scope shrink.

I'm looking specifically for a technical-only consideration of realistically achievable efficiency. Whether there is a market for it isn't important in this regard. Edited to make it more clear.

transonic is awful no matter what

That's... Thanks for trying to help, I guess. That's the conventional wisdom I've mentioned, what we've all been told forever ago. Lately I'm coming upon increasingly more information that leads to me question it. From recent QSST studies, it appears that the "sonic barrier" simplification might no longer hold for some modern laminar and supercritical airfoils, being replaced by a gradual performance reduction across the transonic region, possibly with even less dip than my green line. It's still something I'd wait to hear more independent confirmation on before subscribing to it, though.

I'm very sceptical about SNLF. It works on the tiny, non-lifting fin below an F-15, but scaled up to a real aircraft and on a lift-producing wing, the high Reynolds number will not leave much laminar flow. Mach 1.4 allows for less sweep and a simpler intake, but I cannot say whether this is worth it.

Thanks for the comment. So perhaps not expect much from SNLF. That still leaves the suitability of a widebody fuselage, as inefficient layouts have been another problem for SST. I was actually waiting for you as someone who could probably provide the most insight on the question.

Sweep is needed most for dealing with the trans-sonic hump. Less wing sweep is actually slightly more desirable at m2-m3. Also there is substantial decrease in drag coefficient mach 2 compared to m1.2; m1.1 still creates a sonic boom, really once you are dealing with anything over m1.0 there is no point limiting design speed other than material limits, eg m3 heat will soften aluminum.

Am I the only one who read "SST" as "Single Stage To"?

Only for a business jet.
The high end of the business jets has been in a race for higher cruise Mach numbers which has resulted in a top speed of Mach 0.935 so far (Gulfstream 650, Cessna Citation X). So there seems to be a market value for the top spot in cruise Mach. To improve this further, and substantially, the jump to supersonic speed is unavoidable. So far, the expense of developing such an aircraft for a rather small market has been too high.
On the other hand, a Mach 1.4 design will be much easier than one flying at Mach 2.0. The reasons are:

Intake complexity: At Mach 1.4 a simple pitot intake with a single straight shock has acceptable losses, while Mach 2 demands a complex, adjustable intake with ramps producing a cascade of oblique shocks.
Wing aspect ratio: In order to keep the wing's leading edge subsonic, a Mach 1.4 design can get away with 45° sweep while a Mach 2 design needs at least 60° sweep. The Mach 1.4 wing will be much better for take-off and landing, and for the subsonic legs of the trip.

On the other hand, transport performance at Mach 1.4 will only be ⅔ of that at Mach 2 for comparable L/D, so the Mach 2 design will win hands down if airliner economics are used to evaluate a design. As you said, if you venture into supersonic territory, you might as well go all the way to Mach 2 in order to optimize the profitability of the design. Mach 2 still allows to use a fixed-geometry wing and aluminium, so the overall complexity of the resulting design is still manageable. Beyond that, you need to buy more speed with increasingly more system complexity.
Dietrich Küchemann proposed an empirical formula for maximum supersonic L/D: $$\frac{L}{D}_{max} = \frac{4\cdot(M_{\infty}+3)}{M_{\infty}}$$
Using this as a yardstick will result in 12.5 at Mach 1.4 and 10 at Mach 2. Combine this with the Mach number in order to have something close to transport efficiency, and the Mach 2 design enjoys a hard-to-beat 14% advantage in economic value.
So the only sensible reason to design for Mach 1.4 is to capture the high end of the business jet market, where airliner economics don't apply but bragging rights at the golf course are more important.

On transport performance, my concern was that Mach 2 SST were stunted by low passenger capacity. At just 2/3 of Concorde's weight a 757 carries 200+ passengers. I'd expect a low-Mach transport to come much closer to subsonic pax/ton ratio. Or do you think a M2 jet can also work efficiently with low enough slenderness for say a 3-3-3 configuration, without a major weight penalty?

@Therac: When Concorde was conceived, it was designed for the passenger count of the biggest airliners of its days. By enlarging it a bit, the passenger number would be easy to increase. The slower design will have smaller engines and a lighter intake, but the structure would be essentially the same. Therefore, the passenger fraction would be a bit better, but not dramatically so.

Thanks. A couple clarifications, if you don't mind. Does this mean the Concorde's 20:1 slenderness ratio was just a product of target size, and a much wider 12:1 ratio is good for M2 as well? Also, I assumed different engines for M1.4 and M2, with different bypass rations and exit velocities, and thus different TSFC (0.5 and 0.7 respectively). Would that be incorrect?

@Therac: TSFC goes up with Mach. The values for Mach 1.4 and 2.0 cannot be compared directly. And of course can the fineness be reduced, but then L/D goes down.

Yep, that's why I used TSFC=Ma*0.35 in the question; with that, lower mach gives ~1.6x less fuel per seat-mile and 0.85 another 2.3x over that. I'll try and do some economic math later, but for that - would ground hours per flight most likely stay constant for a faster plane?

why are we ignoring the fact that a faster plane can get away smaller? we don't want to end up with a supersonic analogy to the A380, do we?

@Abdullah: Given the time spent in subsonic flight and on the ground, the step from Mach 1.4 to Mach 2.0 is insignificant for total fleet usage. Yes, a fleet of Mach 2 airplanes will have an optimum for slightly lower seat counts, but I doubt that this will keep the size of the overall aircraft below the one optimized for Mach 1.4.

@PeterKämpf "Airlines operating the A300 on short haul routes were forced to reduce frequencies to try and fill the aircraft. As a result, they lost passengers to airlines operating more frequent narrow body flights."

Mach 1.4 should also reduce the peak intensity of the sonic boom compared to Mach 2, as the principal supersonic drag rise is due to wave drag. And being a small bizjet certainly helps there too. As Concorde found out, there is little point in making a technically viable plane if it is not allowed to fly at its design speed.


text:
How long do airliner tires last? Can this be improved?
I imagine that the tires on commercial jets wear out pretty fast with all those squealing landings as the tire suddenly has to spin up from zero to the speed of landing.
2 questions:
How many landings does any average commercial airliner tire last before it is discarded?
Before landing, why not have a small motor assembly on the landing gear to spin up the tires to the correct speed? Surely this would avoid the degrading tire burn. The tire might last a lot longer and might even offset the cost of the motor assembly.

This has been proposed many times and, I think, tried a few times through the years. Why it's not been adopted I don't know. Perhaps cost benefit? Would carrying the weight of a motor and it's maintenance cost negate the savings. What would be the savings? I seem to remember being told that the major wear of tires is not the spin up wear. Just as info, 747 tires were filled with pure nitrogen at 225psi as I recall.

... probably too many motors, to much added weight, invest and maintenance cost. Plus, a serious danger of skidding in case of a partial malfunction.

I've wondered why aircraft wheels don't simply have vanes on the wheels to spin them up when the gear are lowered. Commercial jets are going pretty fast on landing.

Related: http://aviation.stackexchange.com/questions/3702/why-are-aircraft-tires-not-pre-spun-prior-to-landing-to-preserve-them

@Terry: Spinning wheels add gyro effects. I guess lining up your 747 with the runway on final is much harder when the 18 spinning wheels add their roll-yaw-coupling.

@PeterKämpf It certainly would have some effect. I can see them enforcing some rule, though, that would require delaying turning on the motors until you were lined up, which would then cause a rule that you had to fly at least a 5 mile final to give the lightweight motors time to do it, which would then add more criticism to guys like me who felt that a long, stabilized final was not always necessary or desirable. My vote is for sticking with the old way, and putting up with the occasional blown tire when you get a real greaser on standing water.

I've heard that airliners' tires will last about 200-250 depending on how many hard landings are made. Bizjet tires will last longer, and light aircraft tires will last indefinitely, depending on how gentle you are and what kind of surface you're landing on. I had one start cracking around the wall and just looking unsafe long before the treads ever started to wear.
As for the spin-up idea, it's been proposed many many times, but generally always rejected due to weight and maintenance costs. However, now that fuel is by far the main expense in an airliner's trip, companies are looking for any way to reduce fuel burn. As it turns out, taxiing an airliner burns quite a bit of fuel. They've already started turning one engine off for long taxis, and I think that electric wheel motors will be the next big thing.
The motors have gotten light enough and strong enough that they are a now a viable option. They can be powered by the APU or by a set of batteries (which are also now becoming light enough, see the 787 when they get the kinks worked out). So when they get around to putting them on aircraft for taxiing purposes, you can bet that they'll be spun-up right before landing.

Huh, we have several ultralights in our club, and let me tell those tires do age quickly (all preempted by your gentleness disclaimer, of course).

Related to your last paragraph: http://aviation.stackexchange.com/questions/956/how-does-an-aircraft-taxi

@yankeekilo - I think it just depends on the type of tire, honestly. The tires I put on my plane are fairly thick and heavy, but they're meant to go on trainers and take a beating. I've never seen one wear down to the cords even though I do beat them up sometimes. But then look at the tires on, say, a Citation. They're not much bigger than those on a 172 but they handle many times the weight. I don't know how those last any time at all but apparently they do.

Thanks. Yes, motors are now smaller and more powerful... you might even use them for regenerative braking after the landing...

@ArjunKhosla - Heavy aircraft brakes are mostly hydraulic these days, and I don't see that changing for quite a while. So the power you generate from braking probably wont amount to much, considering how powerful the APU is and how short the braking duration is. However, a few companies are testing electric brakes so you never know.

@Arjun, the regenerated energy must be stored somewhere.  Batteries?  On board batteries are required for safety so landing with batteries low enough to accept the energy recouped from landing is counter to safety.  You would need a heavy bank of batteries for this purpose alone.  It does sound like a good idea but it is not practical with today's technology.

Although tyres can wear out "pretty fast" with numerous landings however as long as the carcass is in good condition then the tyre will go for a retread rather than be discarded.
So from a purely economic point of view I suspect a retread is the cheapest option rather than trying to develop elaborate systems to extend the life of the tread. The other issues I can see with spin up motors is lack of space and temperatures. There is very little room inside a wheel rim for any motors, they are filled with multi-plate disc brakes. The brakes get very hot when braking and would be a very harsh environment for any motor. So far simpler and cheaper to retread the tyre when it starts to get worn out.

This article would lend a number of roughly 240 landings per set of tires

an A340 will complete roughly 6,000 take-offs and landings, calling
  for about 25 sets of replacement tires

Since some aircraft tires can be remolded and to a large extent recycled they are a fairly decent part. In the end of the day the tires are sacrificial by design, its simply easier and cheaper to replace tires every 240 landings than maintain some complex spin up system or use some pricey material (which may or may not exist) that wears slower.
In response to this half of the question

Before landing, why not have a small motor assembly on the landing
  gear to spin up the tires to the correct speed? Surely this would
  avoid the degrading tire burn. The tire might last a lot longer and
  might even offset the cost of the motor assembly.

Take a look at this similar question but basically in short there are a few issues with pre spinning tires even if the system was viable from a weight standpoint. They did some research on it back in the day and found that pre spinning does not really reduce wear significantly (more on that in the linked answer).


text:
Can a 747 land at Ovda?
Since Ben Gurion International Airport is closed, flights are being directed to Ovda, with a 3000 meter / 9,843 foot runway. Can large passenger jets, such as the Boeing 747, land at such an airport?
I understand that a 747 at MTW needs about 10000 feet to land safely, but it can be done in a pinch at 6000-7000 feet. Would a commercial airliner fly flights to a temporary airport such as Ovda considering the shorter runway (i.e. not emergency conditions)?
Also, if I may ask, in the linked thread a 747 pilot refers to the 747 as "a gigantic replica of the North American F-86". To what might he have been referring?

Landing is not usually the issue, however it might be a bit short for takeoff when fully loaded. I'll check up some of the documents I have and check.

@Qantas94Heavy, factor in a density altitude of 4300ft.

Re F-86: It probably means one random person in the intertubes has the same irrational emotional attachment to two different hunks of metal. i.e. Concorde is exactly like an El-Casco stapler ;-)

A 747 at MTW (assume you mean max takeoff weight) cannot land. The max landing weight is far less than the max takeoff weight. Also, landing distance is always shorter than takeoff.

@SteveKuo Any heavier-than-air craft can always land. It might not be able to land safely, but it can always land (this actually does matter sometimes -- in an emergency, you might need to land higher than max landing weight).

Emirate has scheduled a380 flight in manchester (3048m) and gatwick(~3300m)

Marshall Aerospace has worked on 747s. This requires them to land at Cambridge airport (UK), which has a single 6,400ft runway (1,960m). However, this would be a landing and take-off with no passengers, minimal fuel and probably a stripped-out interior, too.

747 AIRPORT PLANNING DOCUMENT - Boeing seems relevant but I don't understand it :-(
It has charts like this (assuming you want to be able to take off again sometime in the future - otherwise you might run out of 747s quite quickly)

I think there's a landing equivalent if you need to know how much, ... erm ... cargo, to jettison.

Hmm, well let's assume 800,000 lbs takeoff weight, and let's assume that GgD was correct with 4,300 pressure altitude. This hypothetical 747 would need approximately 12,500 feet of runway, with no air conditioning, 20 deg flaps and no wind/level runway. With no other considerations, nope, no 747's for Ovda.

My interpretation of this would be that it would take 11000 feet at 800,000 lbs, still out of limits for takeoff. Landing is probably less.

Another way to look at it that they are limited to about 760,000 lb takeoff weight.

they wouldn't be at takeoff weight when coming in to land (after spending most of the fuel on board) but at least dump some fuel when in emergency

@CGCampbell in planning you typically go the other way. I have X runway and am at Y ft altitude, figure out your max takeoff weight (and consider other limits like ZFW) and determine how much fuel, pax and cargo you can take. If limited you can always limit the number of pax or just take everyone and plan a fuel stop.

Is 760,000lb a realistic weight for a revenue paying flight?

@GdD If you figure 380,000 for the empty airplane and 120,000 for full passengers, that would leave you with 260,000 for fuel, which would get you to anyplace in Europe.

So, given Terry's remarks, GdD pointing out that the density altitude for Ovda is around 4300', and the current B744 Airport Planning Document, we can use the unadjusted (there's also a temperature adjusted version, but you don't need that when you have a density altitude in hand) T/O distance chart for the appropriate engine type (I'm going to use the CF6 version for example's sake) to compute how heavy a 747 out of Ovda can be.  (The chart you need is on page 72 on the PDF, by the way.)
Looking across the chart at the 10,000' line gets you an intersection with the 4000' altitude curve about halfway between 750,000 and 800,000 lbs; let us call this 775,000 lbs for argument's sake.  Since we have a slightly shorter runway and a somewhat higher DA, 760,000 lbs is a reasonable MTOW for a 744 out of Ovda; if you wished to be extra conservative, you could cap your MTOW at 750,000 lbs.
As per PDF page 15 of that same document, the typical operating empty weight of a B744 is about 394,000 pounds.  Adding the 120,000 pounds of passengers Terry quoted onto this leaves you with 236,000 lbs of fuel minimum, which is more than enough to get to anywhere in Europe with fuel to spare.  If you want figures, you can use the payload/range charts on PDF page 55 to get a max range of 4200 miles, which as per the great-circle mapper is enough to get you to anywhere in Europe or Africa, as well as the Indian subcontinent and much of SE Asia and China.
As to the landing half of it, the landing distance charts on PDF pages 94 and 95 can be used, assuming a wet runway, a 4300' density altitude for Ovda, the passenger configuration MLW of 630,000lbs, and the ability to use Flaps 30 (Flaps 25 yields a longer landing distance) we get a runway length of around 8700'; this'd be somewhat tight (you'd want to use max autobrakes and your reversers, and make sure you came over the fence at Vref with a firm touchdown to avoid floating in ground effect), but passenger flights don't land at MLW very often, so it'd be a workable operation.

As a sidenote -- if you're in a B744, you can make it basically anywhere you wish in the world from Ovda with a single fuel stop, so it's not as bad as it sounds.  I actually worked it out with the great-circle mapper; the fuel stops I picked are Keflavik, Iceland for N. America, U-Tapao, Thailand for SEA/JP/AUS, and Beja, Portugal for S. America, btw.

I landed there back from Heathrow in 1994 on an El Al Boeing 747-200 and departed on same a week later. Can't say if a 400 series would get in and out but I don't see why not.

Interesting, thank you!


text:
Why would some flights use props instead of jets?
Two years ago I flew from Tel Aviv, Israel to Tromso, Norway via Riga and Oslo. The Tel Aviv-Riga leg was flown in an A320, and the Riga-Oslo and Oslo-Tromso legs were flown in prop planes, Fokker airplanes I think.
What considerations are used to determine what type of plane will fly for a particular journey?
Obviously the choice would be limited to whatever aircraft the carrier has available, but given reasonable choice of any aircraft that seats the required amount of passengers, what considerations are used to decide on props or jets? Runway size? Fuel efficiency for short / long trips? Weather or temperature (both current and typical)?

Related: Which engine is more efficient between turboprop vs jet?,

Short answer - turboprops are more efficient at lower altitudes

This question devolves into two related questions.
1) When buying or leasing the plane, what is the most economical plane for this route (and other routes that the plane may have to fly) at your airline.  One size does not fit all, what is optimal for one leg may be much less desirable for the next.  "Economical" includes capital costs, maintenance costs, operating costs, and down-time costs.  Are your maintenance facilities proficient on this type plane?  Are your pilots cross trained on this new aircraft?
2) Years later your short term choices are limited to the aircraft in your inventory.  What is the best available aircraft for this flight?  For the entire route? Can this plane fit into the runways at the required airports?  Can the aircraft make the trip without stopping for fuel?  How many passengers have booked this flight in advance? the questions that need to be considered are many.
Short answer:  "Oh, I think I'll fly the Turboprop today" is not how it works.  It is a long involved decision considering multiple factors all leading to what user16230 calls efficiency and what I will call profit.  Same thing measured differently.

This doesn't really answer the question of "what factors make a turboprop more efficient than a turbofan?".  Or to put it another way, aren't turbofan "jet engines" better for everything?  Clearly they aren't, because smaller planes don't always use them.  Not to be too negative, but your whole answer is basically "because economic reasons".  For curious noobs like myself that don't know the design considerations, it's not helpful since I already figured that part out on my own. :/  I guess I'll just up-vode user16230's answer, since that's the kind of thing I was looking for. :P

I believe this question is answered here and a nice comparison can be found here but the short answer is efficiency. If memory serves jets gain their efficiency at high altitude moving fast and generally over a long distance. If you are going on a short hop turbo props will be more efficient overall. This chart provides a nice outline of the difference in efficiency.

As for large piston pounders I am not sure of the efficiency but I would think the cost of keeping one running is high simply based on their age (no one is really making big piston planes anymore as far as i know). History channel has a nice show "Ice Pilots NWT" about a freight/passenger airline that still runs DC-3's and the general issues they have with them many of which is related to finding parts.
That being said not all airlines had the money to jump right into jets when they came out. Lots of turbo-props are still flown simply because there is no reason to replace them.

Also, jets typically require longer runways, prop airplanes generally need much less space, so are used for regional flights.

I don't know why you brought up piston engines, not all props are piston engines. Turboprops are turbines, just like jet engines.

I also talk about turbo props and the comparison I posted via the link is mainly about turbo props.

I'm quite surprised that DC-3 users are having trouble finding parts, given that there are still several thousand flightworthy examples which could be cannibalised for parts if necessary...